1. Field of the Invention
This invention relates to power transmission belts having cogs spaced along their length on at least one side thereof and having a reinforcing fabric over the cogs. The invention is also directed to a method of forming a belt of this type.
2. Background Art
Cog belts are used on a wide range of machinery and in a wide range of environments. Commonly, these belts are used on systems with variable speed transmissions, such as on snowmobiles, scooters, buggies, and other different types of equipment. These systems may use a drive and driven pulley combination, wherein speed variation is effected by varying the effective diameter of the pulleys.
A typical belt in this environment has a compression rubber layer, a tension rubber layer, cogs with cog troughs and crests alternating along the length of the belt in at least the compression layer, and at least one load carrying cord embedded in a cushion rubber layer. These belts are commonly referred to commercially as raw edge single cog belts or raw edge double cog belts.
In a typical manufacturing process for this type of belt, an unvulcanized rubber sheet, having a length greater than the desired length of the completed belt, is pressed against a plain cogged mold, having alternating grooves and projections, with the rubber heated and under pressure, to form a cog pad. The resulting cog pad has cogs spaced lengthwise at a constant pitch and may have one or more plies of reinforcing fabric thereon. The cog pad is placed on a cylindrical matrix installed on a molding drum having grooves and projections thereon, so that the cog pad meshes with the cylindrical matrix. The cog pad is cut and its ends butt-joined. Load carrying cords are wound around the cog pad followed by another rubber layer and at least one layer of reinforcing fabric. The resulting belt sleeve is then vulcanized.
Typically, the cog pad is cut to length by skilled workers that manually count the number of cogs necessary to produce the desired end belt length and mark a cog trough in chalk where a cut is to be made to produce the desired belt length. The cog pad is severed at cogs at both ends using a cutter.
The unvulcanized rubber sheet is exposed by separating the reinforcing fabric at one end of the cog pad. The reinforcing fabric at the other end of the cog pad is processed to protrude from the other end of the cog pad. The cog pad is then wound around a matrix with grooves and projections and the ends of the rubber layer are butt-joined. The ends of the reinforcing fabric are joined in overlapping relationship. The cog pad is ultimately vulcanized.
However, as seen in FIG. 10, manufacture by this method may result in flaws in the form of creases 10 in reinforcing fabric 11 on the exemplary cog belt 12 shown. The crease 10 is developed at a trough 14 between crests 16 on adjacent cogs 18. At a joint 20 produced by an overlying fabric end portion 22 and an underlying fabric end portion 24, the overlying fabric end portion 22 tends to attract the underlying fabric end portion 24 in the region of the trough 14 during vulcanization. This is attributable to the lack of rubber at the joint 20 in the region of the trough 14. As the belt 12 is operated and the trough 14 is repeatedly bent, cracks may develop at an early stage in the belt life at the trough 14 where the crease 10 is located. This crack may grow and ultimately cause failure of the belt 12.